London -LRB- CNN -RRB- -- A Europe-wide scandal over horse meat in products labeled beef spread still further Friday , as UK authorities revealed the results of DNA testing on beef products and raided the premises of three more UK food firms .

Of 2,501 tests carried out on beef products across the industry by noon Friday , 2,472 found no horse meat content above 1 % , the UK Food Standards Agency said .

The 29 positive tests involved seven products sold by five suppliers , according to the Food Standards Agency .

Another 962 tests are still under way , the agency said at a news conference .

Fifteen of the positive tests were for the lasagna products sold by frozen food giant Findus that first triggered the horse meat alert last week .

The others concerned beef products sold by supermarket chains Tesco , Aldi and The Co-operative , and burgers made by catering supplier Rangeland .

Tesco , Asda and Aldi all issued statements saying they are boosting testing on meat products to protect customers , restore confidence and ensure product quality .

Jim Smith , group technical director for Tesco , said the company will `` no longer work with the suppliers who fell below our very high standards . ''

The Food Standards Agency declined to give details of the names or location of the three food premises raided Friday .

Investigations are ongoing , but authorities can not rule out the possibility of arrests , it said .

The latest raids come a day after UK authorities arrested three workers at two meat plants , Farmbox Meats near Aberystywth and Peter Boddy Slaughterhouse in Todmorden , West Yorkshire .

Inspectors toured the plants Tuesday and suspended their permits to operate Wednesday , the agency said .

Meanwhile , authorities in northern England confirmed Friday that a dish had been pulled from 47 school kitchens after tests revealed horse DNA .

The ready-made cottage pie , or shepherd 's pie , came from an external supplier , the Lancashire County Council said .

`` This does not appear to be a food safety issue but I 've no doubt parents will agree we need to take a very firm line with suppliers , '' councilor Susie Charles said in a prepared statement .

Authorities across Europe have been scrambling to get a grip on the crisis over rogue horse meat in beef products .

Fears of mislabeled meat also spread to the sky , where companies that provide in-flight catering in Europe initiated reviews of their suppliers .

LSG Sky Chefs said it has contacted all its meat suppliers in Europe and has asked for written confirmation that their products do not contain horse meat . Another major caterer , Gate Gourmet , is doing the same with its suppliers .

The European Union intends to begin testing meat across all 27 member states , it confirmed Friday .

It called for testing 10 to 150 samples per country and at least five tests per country for the presence of the drug phenylbutazone , also known as bute , which is approved for horses but is not allowed to enter the food chain because it can be harmful to humans .

Over the past week , unauthorized horse meat has been discovered in a variety of products labeled as beef that were sold in supermarkets in countries including Britain , France , Sweden , Switzerland , Germany and Ireland .

In the UK , catering giant Compass Group and Whitbread , which owns hotels , coffee shops and restaurants , were the latest to say Friday that they had found horse DNA in certain beef products .

Whitbread said it was removing a meat lasagna and a beef burger from its menus and would work with the Food Standards Agency to implement a robust future testing regime .

`` We are shocked and disappointed at this failure of the processed meat supply chain , '' it said in a written statement .

Compass Group said an affected burger from Rangeland Foods had been provided to some sites in Ireland and Northern Ireland where it holds the catering contract . It promised DNA testing across processed meat products in future .

NorgesGruppen in Norway also confirmed to CNN on Friday that horse meat had been found in frozen lasagna dishes in its stores .

`` The analysis tells us that the lasagnas contained 60 % or more horse meat , '' a spokeswoman said . `` We have withdrawn up to 8,000 products last week . We are in talks with the factory , the French company Comigel . ''

Comigel was one of two French firms whose role in the scandal was highlighted at a news conference held by French authorities Thursday .

The other firm , Spanghero , should have known that the meat it labeled as beef was actually horse , French Consumer Affairs Minister Benoit Hamon said .

Spanghero was the first company to label the meat as beef , the minister said , adding that 750 tons of horse meat were involved over a period of at least six months .

Spanghero should have identified the meat as horse from its Romanian customs code , as well as its appearance , smell and price , he said .

Comigel also should have noticed anomalies in labeling of the meat it received , Hamon said .

A Spanghero representative told CNN the company had acted in good faith . `` The company has never ordered horse meat and we never knowingly sold horse meat , '' the representative said .

The affair has been passed to the Paris prosecutor to be investigated as fraud , Hamon said . The offense is punishable by up to two years in prison and fines of up to â ‚ ¬ 187,500 for the companies involved .

Hamon said there is no reason to doubt that the Romanian abattoir that supplied the horse meat was acting in good faith .

In another twist , UK inspectors said Thursday that horse carcasses contaminated with the equine painkiller bute may have entered the food chain in France . UK and French authorities are working to trace the horse meat , the Food Standards Agency said .

The meat industry was first thrust into the spotlight last month when Irish investigators found horse and pig DNA in hamburger products . The discovery of pig DNA in beef products is of particular concern to Jews and Muslims , whose dietary laws forbid the consumption of pork products . Jewish dietary laws also ban the eating of horse meat .

CNN 's Claudia Rebaza , Kendra Wates and Susannah Palk contributed to this report .

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UK inspectors report 29 beef products test positive for horse meat out of 2,501 sampled

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Food inspectors and police raid three more UK food premises

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Horse DNA is found in dinners supplied to 47 schools in northern England

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The discovery of horse meat in beef products has put Europe 's meat industry in disarray